The present invention concerns a lubricating system for large diesel engines wherein the cylinder lubricating oil is applied to the cylinder surface through a number of nozzles as a mist of oil droplets. A system of this type is known e.g. from WO 00/28194.
The oil supply to individual nozzles occurs by means of a conventionally timed lubricating apparatus from which small piston pumps sends sized portions of oil out to each their nozzle through a valve.
One lubricating apparatus supplies one engine cylinder, or a group of engine cylinders, and is often driven directly by the diesel engine and synchronously with it as the mentioned oil portions are to be dosed to the cylinder surface with timing, i.e. at certain points of time. The lubricating apparatus is usually placed at some distance from each individual point of lubrication. In very long pipes, the compressibility of the oil has a decisive influence on the precision of the dosing. Even though experience with the system has shown that in pipe lengths up to 6-7 meters no great deviations in dosing precision seemingly occur, it is always an advantage with as short pipe lengths as possible between the unit determining the dosing amount and the timing and the point of dosing, upon the cylinder wall.
Not all diesel engines enable direct mechanical driving of the lubricating apparatus synchronously with the number of revolutions. Furthermore, there is an increasing need for a flexible and easy adapting of the dosed cylinder lubricating oil amount for the actual immediate need of the engine, depending on diverse measurable engine parameters. It is also desirable continuously to adapt the timing according to the actual operating situation in a flexible way. All these adaptations are preferably to be controlled centrally.
Driving the lubricating apparatuses synchronously with the engine rpm is possible electronically but is comprehensive and costly. The timing may be immediately changed with such a system.
As the cylinder lubricating oil is to be dosed with one portion per motor revolution, the only possibility for adjusting the dosing is to change the stroke of the pumps. A system for this is described in DK patent application 4999/85. This system is using a cam mechanism for adjusting the pump stroke in dependence of the motor load. Change in this dependence may only occur by exchanging the cams with new cams with another transformation function.
It has also been suggested to adjust the pump stroke by means of a controllable motor, e.g. a step motor. This has been used for point lubrication but the latter is only implemented with difficulty in connection with conventional lubricating apparatuses.
In connection with traditional cylinder wall lubrication, it has been practice until now to use simple spring biased check valves which can resist the internal pressure in the cylinder but are yielding to a slightly higher external injection pressure. In connection with the invention it is desirable and necessary that the valve system only opens at a much higher oil pressure in order that the oil injection from the beginning can assume the character of an atomising injection. It concerns a pressure difference factor of up to several hundred percent.